Each year 1.5 million people visit the orthodontist to have their teeth straightened. During treatment these patients will likely require some space closure or regaining via sliding mechanics. Unfortunately the uncertainty of frictional forces complicates the practitioner's best efforts to move teeth. Consequently, the patient's well-being is somewhat compromised by enhancing the likelihood of dental carries, inflammation, etc.-- all as a result of increased treatment time. The traditional problem is further complicated by the addition of new materials that practitioners know little about with regard to their sliding mechanics. The combination of these two problems presents investigators with the opportunity to address both problems with a common goal: That tooth movement could be better managed if a systematic scientific approach were coupled with the practice of orthodontics. As a first step to improve the delivery of daily care to millions of orthodontic patients, an in vitro investigation of second-order sliding mechanics is proposed. Given that sliding mechanics involves two configurations, one in which clearance between archwire and the bracket exists and another in which no clearance exists, a demarcation point can be identified that is dependent on the geometry of the archwire-bracket combination. Using a three-tooth model, the resistance to sliding will be measured in both configurations in order to delineate the demarcation boundary and the frictional magnitudes in the dry and wet states. Novel materials (titanium brackets and composite archwires) and conventional orthodontic materials (stainless steel, nickel-titanium, beta-titanium, polycrystalline alumina, and single crystal sapphire) will be measured. To assess the influence of geometric dimensions on the sliding proficiency, the critical contact angle, the intrabracket dimension, and the interbracket distance will be measured with clinical appliances by simulating the closure of diastemas or serial extraction sites. The influence of four key biomaterial parameters (hardness, yield strength, elastic modulus, and surface roughness) on the resistance to sliding will also be measured by using or modifying existing archwire materials. From these outcomes simplifying interactions will be identified, and a second-order sliding mechanics model will be devised that is based upon structural mechanics, dimensional analyses, and finite element analyses. Using a panel of clinical experts, these in vitro outcomes will be presented and evaluated against their clinical experiences, and future in vivo trials will be proposed. Ultimately the patient will benefit as the practitioner will learn new facts about sliding in order to reduce treatment time and to enhance clinical practice as novel principles guide the state-of-the art of this specialty.